A wide-range tuning flat mid-long wave infrared coherent light source device

Abstract

The application relates to a long-range tuning flat medium-long wave infrared coherent light source device, which comprises a pump laser, an adjustable pump attenuator, an optical parametric oscillator (OPO), a long-pass filter, an adjustable infrared attenuator group, a motorized rotary table, a motorized rotating wheel and an upper computer. The pump laser is used for generating pump laser; the adjustable pump attenuator is used for adjusting pump light energy; the OPO is used for generating medium-long wave infrared light; the long-pass filter is used for filtering remaining pump light; the adjustable infrared attenuator group is located on the motorized rotating wheel and is used for compressing the change range of output energy of different wavelengths in the tuning process; the motorized rotary table is used for realizing angle tuning of the OPO; and the upper computer is used for controlling the motorized rotary table and the motorized rotating wheel. The application can compress the change range of output energy of different wavelengths in the tuning process of the medium-long wave infrared light source, realize flat tuning output, and is suitable for the application requirements of special occasions such as infrared imaging and biological detection.

Description

Technical Field

[0001] This invention relates to the field of mid- and long-wave infrared laser technology, specifically to a wide-range tuned flat mid- and long-wave infrared coherent light source device. Background Technology

[0002] The mid-infrared band typically refers to the electromagnetic spectrum region with wavelengths ranging from 2.5 to 25 μm (wavenumber 4000-400 cm⁻¹), situated between microwaves and visible light. It can be used not only for detecting molecular content and identifying molecular types but also for molecular-level imaging. Furthermore, in military operations, infrared sources in the 3-5 μm band can interfere with heat-seeking missiles, thus preventing missile attacks on the target. Many gas molecules, toxic agents, pollutants, and explosives exhibit characteristic spectra in this band, making mid-infrared technology highly valuable in military, environmental monitoring, medical treatment, and basic research.

[0003] The performance of the aforementioned application systems largely depends on the level of the mid-infrared light source; therefore, a wide-range tunable mid-infrared coherent light source is a key component of these systems. Conventional lasers are mostly fixed-wavelength lasers, meaning that the laser emitted by a single laser contains only one or a few fixed-wavelength laser outputs, such as the 3.39μm wavelength laser emitted by a He-Ne gas laser, and the 9.6μm and 10.6μm wavelength lasers emitted by a CO2 gas laser. Wavelength-tunable lasers can be divided into two main categories: one category is lasers that achieve continuous wavelength variation based on the broadband emission spectrum of the medium combined with wavelength selection technology (frequency selection technology), such as quantum cascade lasers, whose individual device tuning range is generally narrow; the other category is light sources based on nonlinear optical frequency conversion processes, such as optical parametric oscillators based on non-oxide crystals, which can achieve high-precision continuous wavelength tuning over a wide range of 3-17μm; they are simple and compact in structure, can be fully solidified, and can achieve high peak power and narrow linewidth output, making them one of the important technologies for wide-range tunable infrared coherent light sources. The development of optical parametric oscillators is driven by the demand for tunable laser sources in the visible and infrared light bands.

[0004] Optical parametric oscillators (OPOs) can conveniently achieve frequency conversion to output infrared light of different wavelengths through angle tuning. However, the wide tuning range also means that there are inherently large differences in nonlinear coupling efficiency and quantum efficiency at different output wavelengths, which can lead to significant fluctuations in output energy during tuning, thus affecting the flatness of the light source's output energy. Currently, the output flatness of 3-17μm ultrawide-range tunable OPOs cannot meet the requirements of special applications such as infrared imaging and biological detection. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a wide-range tunable, flat mid-to-long-wave infrared coherent light source device. It utilizes the frequency conversion effect of a pump laser and a nonlinear crystal to generate mid-to-long-wave infrared light. An electric rotary stage controls the rotation of the nonlinear crystal, achieving tunable output of the mid-to-long-wave infrared light. A tunable infrared attenuator array compresses the range of output energy variation at different wavelengths during tuning. This invention can be applied to infrared imaging and biological detection fields, overcoming the drawback of excessive output power fluctuations in 3-17μm ultrawide tunable light sources.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0007] A wide-range tuned flat mid-to-long-wave infrared coherent light source device includes a pump laser and an adjustable pump attenuator, an optical parametric oscillator (OPO), a long-pass filter, an adjustable infrared attenuator group arranged sequentially along the output direction of the pump laser, as well as an electric rotary table, an electric rotary wheel, and a host computer.

[0008] The pump laser emits pump light;

[0009] The adjustable pump attenuator is used to adjust the energy of the pump light incident on the OPO;

[0010] The OPO contains a nonlinear crystal, which is used to excite near-infrared signal light and mid-to-long-wave infrared light from the pump light input into it, and to make the near-infrared signal light oscillate in the cavity and the mid-to-long-wave infrared light be transmitted and output.

[0011] The nonlinear crystal is mounted on an electrically driven rotary table;

[0012] The long-pass filter is used to reflect excess pump light and transmit mid-to-long-wave infrared light;

[0013] The adjustable infrared attenuator assembly includes multiple sets of attenuators, which are respectively mounted on various mounting stations of the electric rotary wheel.

[0014] The incident light-transmitting surface of the pump laser, the incident light-transmitting surface of the adjustable pump attenuator, the incident light-transmitting surface of the OPO and the exit light-transmitting surface, and the light-transmitting surfaces of each attenuator on the adjustable infrared attenuator group are all parallel to each other, and each light-transmitting surface is perpendicular to the input pump beam.

[0015] The host computer contains a program module that outputs commands to control the rotation of the electric rotary table, changing the angle θ between the central axis of the nonlinear crystal and the pump beam to output mid- and long-wave infrared light of different wavelengths; it also outputs commands to control the rotation of the electric rotary wheel to replace attenuators with different transmittance, thereby realizing the range of output energy variation of different wavelengths during the compression tuning process and improving the output energy flatness of the mid- and long-wave infrared light source.

[0016] The host computer contains the following program modules:

[0017] Relationship calibration module: used to obtain the correspondence between the selectable transmittance T of each attenuator in the adjustable infrared attenuator group and the wavelength λ based on multiple experimental measurements of wavelength λ, control of included angle θ, and adjustment of selectable transmittance T of attenuator;

[0018] Real-time monitoring and control module: controls the included angle θ to output mid-to-long-wave infrared light of the target wavelength λ; according to the correspondence λ~T, the computer controls the rotation of the electric rotary wheel to change the attenuator of the adjustable infrared attenuator group 5 corresponding to the target wavelength λ, thereby compressing the range of output energy variation of different wavelengths during the tuning process, so as to improve the output energy flatness during the light source tuning process.

[0019] The relationship identification module includes:

[0020] S1: The host computer outputs several sets of instructions to adjust the angle θ between the central axis of the nonlinear crystal and the pump beam, and records the angle θ and the corresponding mid-infrared light energy I in real time.

[0021] S2: Sort the recorded results in descending order of energy I and divide them into several groups from largest to smallest;

[0022] S3: Arrange the data of several sets of included angles θ from large to small and correspond them one-to-one with the selectable transmittance T of the attenuator in the adjustable infrared attenuator group to obtain the correspondence between included angle θ and selectable transmittance T: θ~T.

[0023] S4: Calibrate the relationship model θ~λ between the angle θ between the central axis of the nonlinear crystal and the pump beam and the output mid-infrared light wavelength λ at the corresponding angle. Using the corresponding relationship θ~T obtained from the results of unit S3, obtain the corresponding relationship λ~T between the selectable transmittance T of each attenuator in the adjustable infrared attenuator group and the wavelength λ. The relationship model θ~λ needs to be pre-calibrated and measured according to a cubic polynomial.

[0024] The adjustable pump attenuator includes a half-wave plate as its incident light-passing surface and a Brewster polarizer as its exit light-passing surface, wherein the Brewster polarizer forms a Brewster angle with the pump light.

[0025] The half-wave plate is a parallel plane optical window made of quartz crystal; the Brewster polarizer is a parallel plane optical window made of glass, with a pump light antireflection coating of wavelength 1.064 μm deposited on the substrate; the angle between the normal direction of the incident end face of the Brewster polarizer and the incident pump light beam is 56° Brewster angle.

[0026] The OPO includes an OPO input mirror as its incident light-transmitting surface, an OPO output mirror as its outgoing light-transmitting surface, and a nonlinear crystal therein. The nonlinear crystal is made of non-oxide gallium selenide barium crystal, which serves as a nonlinear frequency conversion medium for generating tunable mid-to-long-wave infrared light.

[0027] The OPO input mirror is a parallel plane optical window with a surface coating. The lens material is glass. The light-transmitting surface facing the Brewster polarizer is coated with a pump light anti-reflection film with a wavelength of 1.064μm, and the light-transmitting surface facing the nonlinear crystal is coated with a near-infrared signal light high-reflection film.

[0028] The OPO output mirror is a parallel plane light window with a surface coating. The lens material is zinc selenide. The light-transmitting surface facing the nonlinear crystal is coated with a near-infrared signal light high-reflection film, and the light-transmitting surface facing the long-pass filter is coated with a 3-17μm mid-to-long-wave infrared light anti-reflection film.

[0029] The long-pass filter is made of zinc selenide and is coated with a near-infrared high-reflectivity film and a 3-17μm mid-to-long-wave infrared anti-reflection film. The light-transmitting end face of the long-pass filter is at a 45° angle to the mid-to-long-wave infrared output beam.

[0030] The pump laser is a commercial neodymium-doped yttrium aluminum garnet (Nd:YAG) pulsed laser, which generates pump light with a wavelength of 1.064 μm.

[0031] The adjustable infrared attenuator is an infrared neutral density filter made of high resistivity germanium material, and the attenuator can be selected with transmittance of 100%, 30%, 10%, 3%, 1% and 0.3%.

[0032] The present invention has the following beneficial effects and advantages:

[0033] This invention utilizes the interaction between a pump laser and a nonlinear crystal to generate mid-to-long-wave infrared light. By using an electric rotary stage to change the incident angle of the nonlinear crystal over a wide range and alter the phase matching conditions, a wide-range tunable output of mid-to-long-wave infrared light with a wavelength of 3-17 μm can be achieved.

[0034] This invention utilizes an array of infrared attenuators with varying transmittances mounted on an electric rotary wheel to improve the output energy flatness of an optical parametric oscillator. It can be applied to specialized fields such as biological detection and imaging, overcoming the drawback of low output flatness in 3-17μm ultrawide tunable light sources. The system is simple, compact, low-cost, and has high conversion efficiency, making it suitable for widespread adoption in practical systems.

[0035] This invention utilizes an electric rotary table and an electric rotary wheel control program to achieve automatic adjustment of the adjustable infrared attenuator group during the tuning process, with high real-time performance.

[0036] The nonlinear crystal used in this invention is a non-oxide barium gallium selenide (BaGa4Se7) crystal, which has a wide transparency band, a large second-order nonlinear coefficient and a high damage threshold. At the same time, the dielectric properties of the crystal ensure the phase matching of the pump light, which is beneficial to achieving efficient output in the tunable mid-to-long-wave infrared band (wavelength 3-17μm).

[0037] The mid-to-long-wave infrared light generation method used in this invention utilizes commercially available pump sources and the excellent optical properties of crystals to achieve wide-range tunable mid-to-long-wave infrared light output, achieving comprehensive performance improvements in tuning range, conversion efficiency, and device structure. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the large-range tuned flat mid-to-long-wave infrared coherent light source device provided by the present invention;

[0039] Figure 2 This is a schematic diagram of the structure of Embodiment 2 of the large-range tuned flat mid-to-long-wave infrared coherent light source device provided by the present invention;

[0040] Among them, 1 is the pump laser, 2 is the adjustable pump attenuator, 21 is the half-wave plate, 22 is the Brewster polarizer, 3 is the OPO, 31 is the OPO input mirror, 32 is the nonlinear crystal, 33 is the OPO output mirror, 4 is the long-pass filter, 5 is the adjustable infrared attenuator group, 6 is the electric rotary table, 7 is the electric rotary wheel, and 8 is the host computer. Detailed Implementation

[0041] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0043] The present invention will now be described in further detail with reference to the accompanying drawings.

[0044] like Figure 1As shown, this invention provides a wide-range tuned flat mid-to-long-wave infrared coherent light source device, comprising a pump laser 1, and a half-wave plate 21, a Brewster polarizer 22, an OPO input mirror 31, a nonlinear crystal 32, an OPO output mirror 33, a long-pass filter 4, and an adjustable infrared attenuator group 5 arranged sequentially in the direction of the mid-to-long-wave infrared output beam. The pump laser 1 is a commercial Nd:YAG pulsed laser used to emit pump light with a wavelength of 1.064 μm. The light-transmitting surfaces of the half-wave plate 21, OPO input mirror 31, OPO output mirror 33, and adjustable attenuator group 5 are all parallel to each other, and each light-transmitting surface is perpendicular to the input pump beam. The Brewster polarizer 22 is disposed between the half-wave plate 21 and the OPO input mirror 31, and the angle between the normal direction of its light-transmitting end face and the incident pump light is the Brewster angle. The long-pass filter 4 is positioned behind the OPO output mirror 33, and its light-transmitting end face is at a 45-degree angle to the pump output beam. The half-wave plate 21 and Brewster polarizer 22 form an adjustable pump attenuator to adjust the energy of the pump light incident on the OPO. The OPO input mirror 31 and output mirror 33 are used to realize the oscillation of the nonlinearly generated near-infrared signal light in the cavity and the transmission output of mid-to-long-wave infrared light. The nonlinear crystal 32 serves as a nonlinear interaction medium to realize a wide range of tunable output of mid-to-long-wave infrared light, and the angle θ between the central axis of the nonlinear crystal 32 and the pump beam is variable. The long-pass filter 4 is used to filter out the residual pump light in the output mid-to-long-wave infrared light. The adjustable infrared attenuator group 5 is used to compress the range of output energy variation at different wavelengths during the tuning process to improve the flatness of the output energy during the light source tuning process.

[0045] Working principle of the device:

[0046] Step 1: Adjust the angle θ between the central axis of the nonlinear crystal 32 and the pump beam, and record the mid-infrared light energy I output from the adjustable infrared attenuation plate group 5 at the corresponding angle in real time; the mid-infrared light energy I can be collected by an energy meter.

[0047] Step 2: Arrange the recorded results of the included angle θ and the corresponding output mid-infrared light energy I in descending order of energy I, and divide them into 6 groups from largest to smallest;

[0048] Step 3: Divide the data of the 6 groups of included angles θ after division into descending order and match them one by one with the selectable transmittance T of the attenuator in the adjustable infrared attenuator group 5: 0.3%, 1%, 3%, 10%, 30% and 100%, to obtain the correspondence between included angle θ and selectable transmittance T θ~T;

[0049] Step 4: Calibrate the relationship model θ~λ between the axis of the nonlinear crystal 32 and the pump beam, and the output mid-infrared light wavelength λ at the corresponding angle. Using the results of Step 3, obtain the corresponding relationship λ~T between the wavelength λ and the selectable transmittance T of the attenuator in the adjustable infrared attenuator group 5. The relationship model θ~λ needs to be pre-calibrated and measured according to a cubic polynomial: λ=A×(θ 3 )+B×(θ 2 The model coefficients are calculated as A, B, C, and D, which are model coefficients that have been pre-calibrated multiple times. Different crystals, different crystal cutting methods, and wavelength errors in spectrometer detection can all cause changes in the model coefficients. Therefore, the model coefficients are not fixed. Here is an example: when using a barium gallium selenide crystal and the angle between the normal direction of its cutting surface and the direction of the crystal principal axis is 43°, the values ​​of A, B, C, and D obtained by fitting the results of a certain spectrometer detection are -0.0045, 0.2051, 10.671, and 1380.8, respectively.

[0050] Step 5: Control the included angle θ to output mid-to-long-wave infrared light of the target wavelength λ; transform the attenuator of the adjustable infrared attenuator group 5 corresponding to the target wavelength λ according to the correspondence λ~T, thereby compressing the range of output energy variation of different wavelengths during the tuning process, so as to improve the output energy flatness during the light source tuning process.

[0051] Example 1:

[0052] Furthermore, manual adjustment can be adopted as in Example 1: in step 1, the angle θ between the axis of the nonlinear crystal 32 and the pump beam is manually adjusted; in step 5, the attenuator of the adjustable infrared attenuator group 5 is changed.

[0053] Example 2:

[0054] Furthermore, based on the device of Embodiment 1 described above, an automatic adjustment solution of Embodiment 2 can also be obtained by setting a mobile device, such as... Figure 2 As shown. A nonlinear crystal 32 is mounted on an electric rotary table 6 (a Sigma OSCM-25YAM ultra-small 5-phase stepper motor automatic platform), and the controller of the rotary table is connected to a host computer. An adjustable infrared attenuator assembly 5 is mounted on an electric rotary wheel 7 (a Soleber SW102C six-hole electric rotary wheel), and the controller of the electric rotary wheel 7 is connected to the host computer. The host computer has a program module that outputs instructions to the electric rotary table 6 and the electric rotary wheel 7 when the program is executed, realizing the following process steps:

[0055] Step S1: Adjust the angle θ between the central axis of the nonlinear crystal 32 and the pump beam through the computer rotary table program interface, and record the angle θ and the corresponding mid-infrared light energy I output at the same angle in real time;

[0056] Step S2: Arrange the recorded results of the included angle θ and the corresponding output mid-infrared light energy I in descending order of energy I, and divide them into 6 groups from largest to smallest;

[0057] Step S3: The data of the 6 groups of included angles θ after division are sequentially matched with the selectable transmittance T of the attenuator in the adjustable infrared attenuator group 8 from large to small, namely 0.3%, 1%, 3%, 10%, 30% and 100%, to obtain the correspondence between included angle θ and selectable transmittance T, θ~T.

[0058] Step S4: Calibrate the relationship model θ~λ between the axis of the nonlinear crystal 32 and the pump beam and the output mid-infrared light wavelength λ at the corresponding angle. Using the results of step 3, obtain the corresponding relationship λ~T between the wavelength λ and the selectable transmittance T of the attenuator in the adjustable infrared attenuator group 5.

[0059] Step S5: Based on the output infrared light wavelength λ, use a computer to control the rotation of the electric rotary wheel 7, change the attenuator of the adjustable infrared attenuator group 5, compress the range of output energy variation of different wavelengths during the tuning process, and improve the output energy flatness during the light source tuning process.

[0060] In practical applications, laser 1 is a commercially available neodymium-doped yttrium aluminum garnet (Nd:YAG) pulsed laser, with its output light serving as pump light at a wavelength of 1.064 μm. A half-wave plate 21 and a Brewster polarizer 22 form an adjustable pump attenuator to regulate the energy of the pump light incident on the OPO. The pump light passes through the OPO input mirror 31 and enters the nonlinear crystal 32, where it undergoes a second-order nonlinear optical frequency conversion to generate mid-to-long-wave infrared light. The incident angle of the pump light entering the nonlinear crystal 32 is changed by an electrically driven rotary stage 6, achieving wavelength tuning of the mid-to-long-wave infrared light output. The OPO input mirror 31 is a parallel planar optical window with a surface coating made of glass. The surface facing the Brewster polarizer 22 is coated with a pump light antireflection film, while the surface facing the nonlinear crystal 32 is coated with a near-infrared signal light high-reflection film. Nonlinear crystal 32 is a novel non-oxide crystal made of barium gallium selenide (BaGa4Se7), with a light-transmitting surface size of 10×7mm. 2The crystal, 20mm in length, possesses a large second-order nonlinear coefficient and a high damage threshold. Simultaneously, its dielectric properties ensure phase matching of the pump light, facilitating efficient frequency conversion to generate mid-to-long-wave infrared light. Wavelength tuning output is achieved by changing the incident angle of the nonlinear crystal. The OPO output mirror 33 is a parallel planar optical window with a surface coating made of zinc selenide. The surface facing the nonlinear crystal 32 is coated with a near-infrared signal light high-reflection film, while the surface facing the long-pass filter 4 is coated with a 3-17μm mid-to-long-wave infrared light anti-reflection film. The long-pass filter 4 is a zinc selenide substrate with a near-infrared high-reflectivity film and a 3-17μm mid-to-long-wave infrared anti-reflection film on its surface. It is used to filter out the remaining near-infrared light and achieve pure mid-to-long-wave infrared light output. The adjustable infrared attenuator group 5 is mounted on the electric rotary wheel 7, which can realize the use of attenuators with different transmittances during the tuning process. The selectable transmittances are 100%, 30%, 10%, 3%, 1%, and 0.3%, which are used to improve the flatness of the output energy during the tuning process.

[0061] The aforementioned device, which utilizes nonlinear effects and external modulation of the output mid-to-long-wave infrared light to realize a wide-range tunable mid-to-long-wave infrared light source, features a wide tuning range and good output energy flatness, making it suitable for research in specialized applications such as biological detection and infrared imaging. This light source is simple, compact, low-cost, and highly efficient, making it suitable for widespread adoption in practical systems.

[0062] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should be considered within the scope of protection of the present invention.

Claims

1. A wide-range tuned flat mid-to-long-wave infrared coherent light source device, characterized in that, It includes a pump laser (1) and an adjustable pump attenuator (2), an optical parametric oscillator (OPO) (3), a long-pass filter (4), an adjustable infrared attenuator group (5) arranged sequentially along the output direction of the pump laser (1), as well as an electric rotary table (6), an electric rotary wheel (7) and a host computer (8). The pump laser (1) emits pump light; The adjustable pump attenuator (2) is used to adjust the energy of the pump light incident on the OPO (3); The OPO (3) is equipped with a nonlinear crystal (32) for exciting near-infrared signal light and mid-to-long-wave infrared light from the pump light input into it, and for making the near-infrared signal light oscillate in the cavity and the mid-to-long-wave infrared light transmit and output. The nonlinear crystal (32) is mounted on an electric rotary table (6); The long-pass filter (4) is used to reflect excess pump light and transmit medium and long-wave infrared light; The adjustable infrared attenuator assembly (5) includes multiple sets of attenuators, which are respectively mounted on each mounting station of the electric rotary wheel (7). The incident light-transmitting surfaces of the pump laser (1), the adjustable pump attenuator (2), the incident light-transmitting surface of the OPO (3), and the exit light-transmitting surface, and the light-transmitting surfaces of each attenuator on the adjustable infrared attenuator group (5) are all parallel to each other, and each light-transmitting surface is perpendicular to the input pump beam. The host computer (8) contains a program module that outputs commands to control the rotation of the electric rotary table (6) and change the angle between the central axis of the nonlinear crystal (32) and the pump beam. θ It is used to output medium and long-wave infrared light of different wavelengths; it also outputs commands to control the electric rotating wheel (7) to rotate and change attenuators with different transmittance, so as to realize the range of output energy of different wavelengths during the compression tuning process and improve the output energy flatness of the medium and long-wave infrared light source.

2. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 1, characterized in that, The host computer (8) contains the following program modules: Relationship calibration module: used to measure wavelengths based on multiple experiments. λ Control the included angle θ、 Adjusting the selectable transmittance of the attenuator T To obtain the selectable transmittance of each attenuator in the adjustable infrared attenuator group (5). T With wavelength λ Correspondence between λ~T ; Real-time monitoring and control module: controls the included angle θ Output target wavelength λ Mid- and long-wave infrared light; according to the corresponding relationship λ~T The electric rotating wheel (7) is controlled by a computer to rotate, changing the wavelength relative to the target wavelength. λ The corresponding adjustable infrared attenuator group (5) attenuator reduces the range of output energy variation at different wavelengths during the tuning process, thereby improving the flatness of output energy during the tuning process of the light source.

3. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 2, characterized in that, The relationship identification module includes: S1: The host computer (8) outputs several sets of instructions to adjust the angle between the central axis of the nonlinear crystal (32) and the pump beam. θ And record the included angle in real time. θ and the output mid-infrared light energy at the corresponding angle I ; S2: Record the results by energy I Arrange in descending order, dividing into several groups from largest to smallest; S3: Combine several sets of angles θ The data, from largest to smallest, correspond to the selectable transmittance of the attenuators in the adjustable infrared attenuator group (5). T One-to-one correspondence yields the included angle. θ With selectable transmittance T Correspondence between θ~T ; S4: Calibrate the angle between the central axis of the nonlinear crystal (32) and the pump beam. θ and the corresponding mid-infrared light wavelength output at the angle λ Relationship Model θ~λ The correspondence obtained using the results of unit S3 θ~T To obtain the selectable transmittance of each attenuator in the adjustable infrared attenuator group (5). T With wavelength λ Correspondence between λ~T The relational model θ~λ It needs to be obtained through pre-calibration measurement according to a cubic polynomial.

4. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 1, characterized in that, The adjustable pump attenuator (2) includes a half-wave plate (21) as its incident light-passing surface and a Brewster polarizer (22) as its outgoing light-passing surface, wherein the Brewster polarizer (22) forms a Brewster angle with the pump light.

5. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 4, characterized in that, The half-wave plate (21) is a parallel plane optical window made of quartz crystal; the Brewster polarizer (22) is a parallel plane optical window made of glass, with a pump light anti-reflection film of wavelength 1.064μm deposited on the substrate. The angle between the normal direction of the incident end face of the Brewster polarizer (22) and the incident pump light beam is 56° Brewster angle.

6. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 1, characterized in that, The OPO (3) includes an OPO input mirror (31) as its incident light-transmitting surface, an OPO output mirror (33) as its outgoing light-transmitting surface, and a nonlinear crystal (32) therein. The nonlinear crystal (32) is made of non-oxide gallium selenide barium crystal, which is used as a nonlinear frequency conversion medium to generate tunable mid-to-long-wave infrared light.

7. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 6, characterized in that, The OPO input mirror (31) is a parallel plane light window with a surface coating. The lens material is glass. The light-transmitting surface facing the Brewster polarizer (22) is coated with a pump light anti-reflection film with a wavelength of 1.064μm, and the light-transmitting surface facing the nonlinear crystal (32) is coated with a near-infrared signal light high-reflection film. The OPO output mirror (33) is a parallel plane light window with a surface coating. The lens material is zinc selenide. The light-transmitting surface facing the nonlinear crystal (32) is coated with a near-infrared signal light high-reflection film, and the light-transmitting surface facing the long-pass filter (4) is coated with a 3-17μm medium-long-wave infrared light anti-reflection film.

8. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 1, characterized in that, The long-pass filter (4) is made of zinc selenide and is coated with a near-infrared high-reflectivity film and a 3-17μm mid-to-long-wave infrared anti-reflection film. The light-transmitting end face of the long-pass filter (4) is at 45° to the mid-to-long-wave infrared output beam.

9. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 1, characterized in that, The pump laser (1) is a commercial neodymium-doped yttrium aluminum garnet (Nd:YAG) pulsed laser, which generates pump light with a wavelength of 1.064 μm.

10. The wide-range tuned flat mid-to-long-wave infrared coherent light source device according to claim 1, characterized in that, The adjustable infrared attenuator group (5) is an infrared neutral density filter made of high resistivity germanium material. The transmittance of the attenuator can be selected as 100%, 30%, 10%, 3%, 1% and 0.3%.

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